The present invention relates to a method and/or architecture for implementing a charge pump generally and, more particularly, to a method and/or architecture for implementing a negative bias charge pump.
A charge pump circuit can generate a high voltage pump output from a single input. Multiple charge pump circuits can be implemented serially to provide increasing voltages. Conventional negative charge pump circuits are built from a clock and capacitor circuit. Ideally, the serially implemented negative charge pump circuits can provide a xe2x88x92(VDDxe2x88x92Vth) increase at each output for a GND to +VDD voltage potential. However, conventional charge pump circuits implement a single substrate (i.e., a single well) for multiple charge pump circuits. The source node voltage is degraded by increasing Vth which is caused by the increased body bias. As subsequent charge pump circuits are added, the source node voltage is degraded due to increasing body bias voltage. Since conventional negative charge pump circuits have high body bias voltage, the output voltage is limited. Additionally, negative charge pump circuits are limited by the technology in which they are implemented. For example, one could not implement a positive charge pump with a P-type substrate and without a twin well process.
Conventional charge pump circuits implement multiple stages in a single substrate. The bulks of each of the transistors within the stages acquire a large body bias voltage. Additionally, for each consecutive stage, a higher body bias voltage builds. For example, a source node can be at approximately xe2x88x922VDD, while a ground node may have xe2x88x922.5 volts of body bias voltage. The body bias voltage can degrade a threshold voltage of the conventional charge pump circuits. The body bias voltage can degrade voltage level of a charge pump output. The body bias voltages cause diminishing returns of conventional charge pump circuits. Conventional charge pump circuits can require ten or more stages to provide the desired return. The absolute negative voltage capable of being generating by conventional charge pump circuits is limited by body bias voltage.
The present invention concerns an apparatus generally comprising a plurality of pump stages each implemented on an independent well. The plurality of pump stages may each be configured to generate an output voltage. The plurality of pump stages may be serially connected such that a body bias voltage input of one stage is received from the output voltage of a previous stage.
The objects, features and advantages of the present invention include providing a method and/or architecture for implementing a negative bias charge pump that may (i) provide increasing levels of negative output voltage, (ii) allow a relatively large negative output voltage to be developed from a smaller negative bias voltage and/or (iii) implement an independent well for each negative charge pump circuit.